Synchronous dynamo-electric machine



Nov. 18, 1930. .1. F H. DOUGLAS ET AL SYNCHRONQUS DYNAMO ELECTRIC MACHINE Filed April 27, 1925 Patented Nov. 18, 1930 UNITED stares Application filed April 27, 1925.

Our invention relates to dynamo electric machines of the synchronous type, and more particularly to field magnet structures in which the winding is distributed. In machines of this type previously made, the pole face has either been made concentric with the armature surface or with the several members diverging from the armature surface toward the outer part of each portion of the 0 poles. The latter of these two forms is much superior to the first in its wave form of induced electromotive force, in that sudden and rapid changes in the magnetic flux density opposite the openings over the exciting coils is largely avoided. However, the wave of induced voltage of the latter form is by no means a sine Wave and shows marked de fects which cause undesirable noise in telephone circuits adjacent to lines to which such machines are connected. The deviation of the voltage from a sine wave may be traced to a deviation of the flux density on the armature surface from a sinusoidal distribution in such a manner that considerable components or harmonics of noise-producing qualities, or high frequency as compared to the useful current, are present.

In order to improve the magnetic flux dis- 'tribut-ion, we shape the pole faces as follows: 30 The contour of the pole face is shaped so that under each member of the pole the gap is varied approximately inversely as the sine wave or other desirable wave or flu distribution. Thus thegap under each member farthest from the pole center is to the gap nearest the pole center inversely as the flux densities desired opposite these points, and not as the magneto-motive forces of the coils. The result is that the inclination of the central member is somewhat less than known forms and the divergence of the outermost members somewhat more. Moreover, we shape the outer members with a greater curvature than the center members so that at intermediate points the desired flux distribution Will be had. l/Ve find that these departures from usual practice decidedly improve the flux distribution and the wave of induced electromotive force, and hence the efficiency of machines of this type.

' The armature winning rarest orricr.

IvIE. "\VAUKEE, WISCONSIN MACE-ZINE Serial No. 26,113.

We make the gaps on either side of the coil openings unequal. but in the ratio of the available magneto-motive forces on the two faces. However, instead of making the ap at the inner corner on an outer pole member equal to the gap at the center of the pole we make them in direct ratio as the magnetomotive forces at these two places, and in inverse ratio as the sine wave or other desirable wave of flux distribution.

The coil spacers or retainers 011 the neutral axis are made of non-magnetic material to avoid their effect of diverting magnetic lines from the armature. The pole tips of opposite polarity most nearly approaching each other are extended until they (the pole tips) are approximately as close to the neutral axis as they (the pole tips) are to the equivalent armature surface. The pole face ofthe outer member adjacent to the pole tips is corrected also for the curvature of the lines of magnetic force in this region.

For best results the corners or tips of each of the outer pole members nearest the center of the poles are made as sharp as possible and with an acute angle so that their sides adjacent to the slot opening are inclined away from the armature and away from the center of the pole.

Having described our invention in general terms, we give for the fuller understanding of our invention the following description in connection with the drawings, in which Fig. l'is a detail elevation of a machine embodying our inventiomparts being shown in section; and Fig. 2 is a section upon the line A-A of Fig. 1. Y

The proper selection of the number of armature slots and coil pitch is important in the design of any alternating current ma chine. By the proper choiceof these factors of design any one or two residual harmonics may be greatly reduced, the ratio of the harmonics left in the voltage to that in the flux being termed belt and pitch differential factors, respectively. Our invention is directed particularly to reduce the harmonics in the flux wave and hence in the voltage wave. does not introduce any new harmonics at no load and the same per cent reduction given by the belt and pitch factors of any given design are obtained with our invention.

At full load the armature reaction introduces harmonics in the. voltage wave not present originally. These are controlled in any case by proper choice of armature Winding and by the ratio of armature to field ampere turns, by methods well mown to this art. Our invention discloses no improvement inthis effect but we rely chiefly on the elimination of harmonics by shaping the field iron, which in itself has an equal effect at no load and full load. I

The spider is 1 and is mounted on a shaft (not shown) in any well-known manner, and supports thepole yoke or core 2. flash pole is divided into pole members 3, e and 5, and is secured to the pole yoke in any suitable manner. The central member 3 is mag.- netically a unit and may be divided. sired, for the purpose of better support. The outer members l and 5 occur, in pairs andmay be termed side members. inc exciting winding is divided -to coils 6, and 8, shown in section and in elevation. lhe inner coil 8 surrounds the center member 3 only; the coil 7 surrounds both members 3 and while the outermost coil 6 surrounds the entire pole. The central part of the pole 3 is thus surrounded by. all the coils; the side members a are surrounded by all the coils except 8; and the outermost members of'the core 5 are surrouneed y only one coil 6. Thus, if the coils are of equal magnetic strength, the magneto ietive force on the faceof member lis tv. cethat on member 5, and the magneto-motive force on member 3 is three times that on the face of member 5.

The armature surface 9 is shown t into slots 10 and teeth 11, the teeth part of the armature core12 whic. is of laminated iron or steel. .he slots etween the teeth serve for su orti g mature coils 13. which "are di posed in any customary or suitable manner. The arr ture core issupp'orted by a frame or yoke in any suitable manner; The actuel armature surface is broken into the teeth (M slots but for the purpose of do r n it is customary to make computations from surface which is assumed to have the same magnetic characteristics as the toothed surface but which is a smooth core surface. 7 p a surface is here indicated by the'line Mel-l. The equivalent smooth armature 14 is located .back of the tips of the armature teeth, the ratio of its distance from the pole face to the distance of the tips of the armature teeth to the pole face being th coefficient, a term well known to deh ners ,f electrical machines; llhe distance of this smooth coresurface from the actual tips of 22 and 23, respectively.

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thedistance from the equivaleit armature surface l l 1 l to tile tips of the teeth 11 is substantially constant. The surface 1919 may, therefore, be assumed as a circular cylinder having as itsaxis tl'lQ'CQllfQl' of the shaft. It is from this equivalent armature surface that magnetic clearances or gaps should bereckoned; lhe faces of the pole members 3, e and 5 are15, 1e

center 18 are 19 and 20; and the corners or tips farthest from the pole center being 21,

By the gap or magetic clearance is meant the distance from any point on the pole face measured in radial direction to the equivalent armature surface. Thus, the gap at 18 is the distance -.d 1'5; the Cw n he an -11 orners 01 tips 0 t eseiaces nearest the ole from face 15 to equivalent armature surface 14 at the point 18'.

The gap at 22 is made twicethe gap at 20 and the gap at 21 is made 3/2 of the gap at 19. However, the gaps l8, l9 and 2f) are not necessarily equal. On the contrary, with the best spacing. of the coils 6, 7 and 8 these gaps will be unequal. I To make the gap at 19 and 18 in direct ratio as the neto-motive forces on faces 16- and- 15, a. inverse ratio as the magneto-motive ice distribution desired at these poii. -f

larly, the gap at 25) is to the'gap at 18 dire. ly as the magneto-motive force 17 is to that on 15, and inversely as the desired ma netic density desired at sired at 18.

The inclination reater than that. "reater than that 20is' to that deof- 16, which is turn ofl5, but with the best of coils 6, 7 and 8' the inclination of 15; less than known forms and that of face 17 is greater thauhnown fori ,VVe shape them by the rule that the at corner 21 ofmember 3 to the at 18 inverse the flux densit desired at 21 is to at 18. Simih is to the gap l9 asthe inte densities at the two points, a. H a similar mar .er are the gaps 23 and 20 proportioned.

By this means not only a smooth wave ob rained, but also one that varies as the sine wave or other desirable wave of flu distribution; I e f The face 17' of the outer members of the poles 5 are given greater curvature than t l e 1 face 16 of member a and that in turn is I i a V of surface l7 is made the where T is the distance from neutral aXi pole member is nearer to the center the po given greater curvature than the fa 5 of member 3, in such manne gap under, each of these y as a sine wave or other desired wave of flux distribution.

Member 2%, which serves to space coils 6 and to retain them in place, is made of noniii-agnetio material, when used, but may be omitted, if desired, providing members 5 have the requisite strength to hold he coils in place without the aid of members 24. The neutral plane taken along the line ll A is shown by its trace; it is a magnetically neutral plane located halfway between opposite poles. The pole face 1? of the outer members 5 adjacent to the pole tips 23 is prolonged until the pole tips are approximately as close to the neutral axis i l--21 as they are distant from the armature surface 14. The face 17 of members 5 may not be laid out exactly by the simple rule that the gap is made to vary inversely as the desired flux density, but a slight correction is desirable when the desired flux density along the armature surface 14 varies less 'dly than the distance from the neutral axis, as is the case with a sine wave, the pole face 17 adjacent to the tip 23 is brought slightly closer to the armature surface, and vice versa.

Since the sine wave of flux density is re nized as the best, the best shape of pole is that in which the distance from the arm ture surface varies according to the following equation: Let the distance from the tral axis to point on the equi talent a1: ture surface be X, and the distance from that point to the pole'face be Y, on which the magneto-motive force is F If the gap the pole center is G and the magneto-mot, -76

force on that be F, then the gap at the point X is co fa Inf to neutral axis on the equivalent armature surface or the pole pitch, the pole face being corrected for curvature in the lines of force near the pole tips. It will be understood that the above equation holes for the pole face up to the tins; that is, as long as Y is less than the distance to the interpolar axis.

For the best results the corners tips 19 and 20 of pole members at Z111l5 are mad with ;as sharp a curvature as is possible, and

formed to an acute angle so that the under surfaces 26 and 5 adjacent to the slot, are inclined an angle away from corners and away from the center of the pole, the best angle being not materiall r greater than 15 degrees.

F or the best results the slot opening between the poles 3 and 4 and a 5 should be narrow so that the inner tip an ou than the outer tip of the pole member inside and next adjacent to it, but good results are obtained when the inner tip not farther from the pole center than the outer tip of the next adjacent inner pole member by more than half of the smallest clearance between the pole and the armature at that point.

We show a machine with twelve poles and with a field winding divided into three coils per pole, dividing the pole core into five portions, but it is evident that it isnot limited to any number of poles or any number of coils per pole. The modifications needed in any case are clearly set forth in the specification as to their guiding principle. e aim in the appended claims to cover all modifica tions which: do not depart from the spirit and scope of our invention.

The armature vinding shown in the drawing is that customarily used, namely, one in which the armature winding is disposed in several slotsper pole perphase, but any desirable armature winding may be used in connection with our invention.

By the term desired wave of flux distribution we mean a Sine wave, or one which does not deviate therefrom at any point more than 10%, nor deviate therefrom in such a manner as to causeobjectionable telephone inte 'erencc.

What we claim as our invention is:

1. The combination with the armature of a dynamo electric machine, 'of afield magnet having a distributed winding comprising a plurality of coils for each pole, and pole mem bers, each member of the pole so shaped with reference to its adjoining member that airgaps on the two 'sides'of any coil separating adjacent pole members are to each other as the magneto-motive forces on the respective faces of said pole members.

2. The combination with the armature of a dynamo electric machine, of a field magnet having a distributed winding comprising a plurality of coils for each pole, and poles, each pole comprising plurality of members including outer pole members, the corners of each outer pole member nearest the pole center being formed to a relatively sharp and acute angle that is, an an le not materially greater than 45. i

3. The combination with the armature of a dynamo electric machine, of field magnet having a distributed winding comprising a plurality of coils for each pole, and poles, each pole comprising; a plurality of members, including outer pole members, the at the inner tip of each outer pole member being less than the gap at the central part of the central pole member.

l. The combination with the armature of a V dynamo electric machine, of a field magnet 1 plurality including outer pole members, the tips of said outer pole members nearest the pole center being distant from the equivalent armature surface, when compared with the 2.1) at center ofthe pole in the direct ratio of the magneto-motive forces on these tips to the magneto-motive force on the center of the poles and "n inverse ratioof the values of the desired wave of flux distribution at these points. a

5. The combination with the armatureof a dynamo electric machine, of a. field magnet having a distributed winding comprising a of coils for eachpole, and poles, each pole comprising a plurality of members including outer pole members, the gap at the inner tip of each outer pole member being less than the gap at the center part of the central pole member, and the outer pole tip of each outermost pole member approaching the neutralaxis at a distance not greater than its distance from the equivalent armature surface. v

6. The combination with the armature of a dynamo electric machine, of afield magnet having a distributed winding comprising a plurality of coils for each pole, and poles, each pole comprising a plurality of members including outer pole members, the inner tips of said outer pole members being formed with r a relatively sharp acute angle (not materially greater than and the distance of each tip from the equivalent armature surface be ing less thanthe distance from the central part of the central pole member, and the outer'pole tip of each outermost pole member approaching the neutral axis at a' distance not more than its distance from the equivalent armature surface; v

" 7. The combination with the armature of a dynamo electric machine, of a field magnet having a' distributed winding comprising a plurality of coils for each pole, and poles,

each pole comprising a plurality of spaced pole members, said pole members arranged to project over the coil'sso that the inner tip of each of the outer pole members is substan tially as close to the center of the pole as the outer pole tip of the adjacent inner pole member.

8. The combination with the armature of a dynamo electric machine, of a field magnet having a distributed winding comprising a plurality of coils for each pole, and poles comprising a plurality of pole members including outer pole members, the curvatures of the faces of the pole members differing so that the curvature of the face of an outer pole 'member is greater than that of an adjacent inner pole member.

9. The combination with the armature of a dynamo 'electric'machine, of a field magnet having a distributed winding comprising a plurality of coils for each pole, andrpoles comprising a plurality of pole members ineluding outer pole members, the curvatures of the faces of the pole members differing. so i tures. v

JOHN F. H. DOUGLAS. EDWARD KANE. 

